Boris Yeltsin was making a presidential visit to Washington in 1995 when he was found one night outside the White House dressed only in his underpants. He explained in a slurred voice to US secret service agents that he was trying to hail a cab so he could go and buy a pizza. The following night he was discovered by a guard, who thought he was an intruder, wandering drunkenly around the basement of his official residence.

Drunk or sober, Yeltsin and his escapades became the living symbol for the world, not just of the collapse of the Soviet Union but of a dysfunctional administration in the Kremlin and the decline of Russia as a great power. It was impossible to take seriously a state whose leader was visibly inebriated much of the time and in which policy was determined by a coterie of corrupt family members and officials serving at Yeltsin’s whim.

Donald Trump is often compared to Vladimir Putin by the media which detects ominous parallels between the two men as populist nationalist leaders. The message is that Trump with his furious attacks on the media would like to emulate Putin’s authoritarianism. There is some truth in this, but when it comes to the effect on US status and power in the world, the similarities are greater between Trump and Yeltsin than between Trump and Putin.

Trump does not drink alcohol, but his incoherent verbal onslaughts on Australia, Mexico and Sweden since he became President are strongly reminiscent of Yeltsin’s embarrassing antics. Both men won power as demagogic anti-establishment leaders who won elections by promising to reform and clear out corruption in the existing system. The result in Russia was calamitous national decline and the same thing could now happen in America.

It will be difficult for the US to remain a super-power under a leader who is an international figure of fun and is often visibly detached from reality. His battle cry of “Fake News” simply means an inability to cope with criticism or accept facts or views that contradict his own. World leaders who have met him say they are astonished by his ignorance of events at home and abroad.

This cannot go on very long without sizeably diminishing American global influence as its judgement and actions become so unpredictable. Over the last three quarters of a century, countries of all political hues — dictatorships and democracies, republics and monarchies — have wanted to be an ally of the US because it was the most powerful player in world affairs.

It will remain so but the degree and nature of its primacy is changing significantly for four reasons. The US has a leader who appears unhinged to an extent not true of any of his predecessors. Secondly, political combat in the US has reached an all-absorbing ferocity not seen since the 1850s. This does not mean that the last act of this crisis will be a civil war, but American society is more divided today than at any time since the conflict between North and South. From the moment Trump took office he has shown no inclination towards compromise and his divisiveness inevitably makes America becomes a lesser power than it was.

The US is in a much stronger position today than the Soviet Union in 1991, but aspects of the two situations are the same. The Soviet Union was past its peak when it dissolved, but the US is weaker than it was fifteen years ago. Despite its vastly expensive armed forces, the US has failed to win wars in Afghanistan and Iraq or to obtain regime change in Syria. In all three wars, it made serious mistakes and suffered important setbacks. Barack Obama had an acute sense of just how far US military strength could be turned into political gains without stumbling into unwinnable wars in the Middle East and beyond. Contrary to Trump’s jibes about Obama doing disastrous deals with Iran and others, the last president kept out of the Syrian civil war, which would have been as draining as Afghanistan or Iraq, and gave priority to the campaign to eliminate Isis.

As presidential candidate Trump presented himself as an isolationist, claiming to have opposed the wars in Iraq and Libya. He had taken on board, as Hillary Clinton had not, that the American public does not want to fight another ground war in the Middle East. But Trump’s appointment of two senior generals — James Mattis as Defence Secretary and HR McMaster as National Security Adviser — tells a different and more belligerent story. Already, there are steps being taken to create a Sunni Arab coalition, led by Saudi Arabia and the Gulf monarchies and in cooperation with Israel, to confront Iran.

The Trump administration does not have a coherent foreign policy and will probably go along at first with many of the policies already in place. The dangerous moment will come later when it has to devise its own responses to new events, such as terrorist attacks by Isis, and its real capacity becomes apparent. It looks all too likely that a president who has such a ludicrously warped picture of life in Sweden will fail to grapple successfully with complex crises in Yemen, Syria or Iraq.

The election of Trump brings with it another negative but less tangible outcome that is already eating away at American primacy: the US will be not only divided but unable to focus on for the foreseeable future on anything other than the consequences of Trumpism. When US politicians, officials and media look at Russia, China, Ukraine, Iran, Israel or anywhere else in the world from Sweden to Australia, they will view them through a prism distorted by his preconceptions and fantasies.

The US is not alone in this. The debilitating result of a single factor marginalising other crucial issues has become all too clear in Britain since the Brexit vote. Tony Blair said in his recent speech that “this is a government for Brexit, of Brexit and dominated by Brexit. It is a mono-purpose political entity.” Aside from this single-minded focus, nothing else really matters, not the health service, the economy, technology, education, investment or crime. “Governments’ priorities are not really defined by white papers or words, but by the intensity of focus,” explained Blair. “This government has bandwidth for only one thing: Brexit. It is the waking thought, the daily grind, the meditation before sleep and the stuff of its dreams; or nightmares.”

In the US, Trump is a similarly obsessive concern. Once it was smaller European countries like Ireland and Poland that were derided for an exaggerated and unhealthy preoccupation with their own problems. A Polish joke from the 1920s relates how an Englishman, a Frenchman and a Pole competed to write the best essay on the elephant. The Englishman described “elephant hunting in India”, the French wrote about “the elephant in love” and the Pole produced a lengthy paper on “the elephant and the Polish Question”. These days the Englishman would undoubtedly write about “the elephant and Brexit” and an American, if he was allowed to enter the competition, would write interminably about “the elephant and Donald Trump”.